This study will focus on the appearance of the vascular component of the myocardium in diabetic patients; in particular, it will be the aim to assess intramyocardial capillary integrity, in order to determine if the characteristic microangiopathy, associated with the diabetic condition, which has been described, among others, in the renal and skeletal musclar compartments, can also be observed in the diabetic heart. We intend to examine with the electron microscope the microvasculature within biopsied myocardial tissue in diabetic patients. Specifically, changes in capillary basal laminae will be investigated and measurements of their thickness will be recorded. An attempt will also be made to detect myocardial alterations in general, and capillary abnormalities in particular, under the controlled conditions of an experimentally-induced diabetic state in rats, and to relate and compare these findings to the human myocardial profile in diabetes mellitus.